OBJECTIVE To compare the efficacy of intrauterine insemination (IUI) and intracervical insemination (ICI) when used by fertile single women in a donor insemination program. METHODS Prospective randomized crossover study. METHODS Donor insemination program (not an infertility clinic). METHODS Single fertile women choosing to inseminate with frozen donor semen. METHODS Clients received procreative counseling and screening and were then randomly assigned to begin office insemination with ICI or IUI. If additional insemination cycles were required, the clients used the method opposite their previous method of insemination until pregnancy was achieved. METHODS Monthly fecundity rate was compared between the two methods of insemination. RESULTS Sixty-two women contributed a total of 189 cycles, 94 by IUI and 95 by ICI. The monthly fecundity rate for IUI was 15%, as compared with 9% for ICI, (P=0.14). When the analysis was confined to cycles in which only one insemination was performed (64 IUI and 65 ICI cycles), the monthly fecundity rates were 14% for IUI and 5% for ICI (P=0.04). CONCLUSIONS Intrauterine insemination with frozen donor sperm is more effective than intracervical insemination for single women without known fertility problems.